The present disclosure relates to interior permanent magnet (or “IPM”) machines such as, for example, an IPM motor. IPM machines have been used in various applications in the past, but the use of such machines in applications requiring a high degree of torque from a relatively small machine or low-noise has been limited by certain characteristics of IPM machines.
For example, because IPM machines utilize a rotor that contains a number of interior permanent magnets, there is a tendency for magnetic flux produced by the magnets to circulate between two adjacent magnets. This intra-magnet flux circulation tends to reduce the overall torque output of the machine because the magnetic flux that circulates between the magnets is not readily available for torque production. In addition to reducing the overall torque output of the machine, this intra-magnet flux circulation also tends to decrease the overall efficiency of the machine.
Further, IPM motors because of their use of discretely positioned interior permanent magnets tend to have a degree of unwanted torque ripple or torque variation often known as “cogging torque.” Such cogging torque can produce unwanted noise and/or vibrations and can reduce the overall efficiency of the machine.
A further characteristic of IPM machines that potentially limits the torque output and efficiency of such machines is the ability to get current into the windings of such machines. The ability to get current into the machine is an important factor in producing torque and having an efficient machine as the torque out of the machine will correspond closely to the amount of current that is put into the phase windings and the speed at which the current its placed in the phase windings will impact the efficiency of the machines. Typically, IPM motors have had a construction that generally results in the phase windings of such machines having a relatively high inductance. This relatively high inductance has tended to limit the ability to get current in to the windings of such machines.
The present disclosure described several embodiments of IPM machines that are designed to address the described, and other, limiting characteristics of IPM machines to provide an improved IPM machine that has, for example, a relatively high torque output, high efficiency and low cogging torque.